“Class II” ozone-depleting substances (ODSODSA compound that contributes to stratospheric ozone depletion. ODS include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, hydrobromofluorocarbons, chlorobromomethane, and methyl chloroform. ODS are generally very stable in the troposphere and only degrade under intense ultraviolet light in the stratosphere. When they break down, they release chlorine or bromine atoms, which then deplete ozone. A detailed list (http://www.epa.gov/ozone/science/ods/index.html) of class I and class II substances with their ODPs, GWPs, and CAS numbers are available.) have an ozone depletion potentialozone depletion potentialA number that refers to the amount of ozone depletion caused by a substance. The ODP is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11. Thus, the ODP of CFC-11 is defined to be 1.0. Other CFCs and HCFCs have ODPs that range from 0.01 to 1.0. The halons have ODPs ranging up to 10. Carbon tetrachloride has an ODP of 1.2, and methyl chloroform's ODP is 0.11. HFCs have zero ODP because they do not contain chlorine. A table of all ozone-depleting substances (http://www.epa.gov/ozone/science/ods/index.html) shows their ODPs, GWPs, and CAS numbers. less than 0.2, and are all hydrochlorofluorocarbonshydrochlorofluorocarbonA compound consisting of hydrogen, chlorine, fluorine, and carbon. The HCFCs are one class of chemicals being used to replace the CFCs. They contain chlorine and thus deplete stratospheric ozone, but to a much lesser extent than CFCs. HCFCs have ozone depletion potentials (ODPs) ranging from 0.01 to 0.1. Production of HCFCs with the highest ODPs are being phased out first, followed by other HCFCs. A table of ozone-depleting substances (http://www.epa.gov/ozone/science/ods/classtwo.html) shows their ODPs, GWPs, and CAS numbers. HCFCs are numbered according to a standard scheme (http://www.epa.gov/ozone/geninfo/numbers.html). (HCFCs). HCFCs were developed as transitional substitutes for Class I ODS and are subject to a later phaseout schedule than Class I ODS.

HCFCs are used in a wide variety of applications, including refrigeration, air conditioning, foam blowing, solvents, aerosols, and fire suppression. Although there are currently 34 HCFCs that are subject to the phaseout, only a few are commonly used. Historically, the most widely used include HCFC-22 (usually as a refrigerant), HCFC-141b (as a solvent and foam-blowing agent), and HCFC-142b (as a foam-blowing agent and component in refrigerant blends). Learn more about common HCFCs and their uses.

Some HCFCs, like HCFC-22, are also a component in refrigerant blends. While these blends are not listed among the 34 controlled HCFCs, they are subject to the same rules because they contain Class II ODS. Common refrigerant blends that contain HCFC-22 include R-401A, R-402A, R-408A, R-409A, R-414B, and R-502A.

The Phaseout of HCFCs

As a Party to the Montreal ProtocolMontreal ProtocolThe international treaty governing the protection of stratospheric ozone. The Montreal Protocol on Substances That Deplete the Ozone Layer and its amendments control the phaseout of ODS production and use. Under the Montreal Protocol, several international organizations report on the science of ozone depletion, implement projects to help move away from ODS, and provide a forum for policy discussions. In addition, the Multilateral Fund provides resources to developing nations to promote the transition to ozone-safe technologies. The full text of the Montreal Protocol (http://ozone.unep.org/Publications/MP_Handbook/Section_1.1_The_Montreal_Protocol/) is available from the United Nations Environmental Programme (UNEP)., the United States must incrementally decrease HCFC consumption and production, culminating in a complete HCFC phaseout in 2030. HCFC usage must be reduced to at least 90 percent below baseline levels in 2015 and to at least 99.5 percent below baseline levels in 2020.

Section 605 of the Clean Air ActClean Air ActA law amended by Congress in 1990. Title VI of the CAA (http://www.epa.gov/ozone/title6/index.html) directs EPA to protect the ozone layer through several regulatory and voluntary programs. Sections within Title VI cover production of ozone-depleting substances (ODS), the recycling and handling of ODS, the evaluation of substitutes, and efforts to educate the public. establishes the U.S. phaseout targets for Class II substances. In 1993, EPA established the phaseout framework and the "worst-first" approach, which focused first on HCFC-22, HCFC-141b, and HCFC-142b because they have the highest ozone depletion potentials of all HCFCs.

The U.S. schedule for meeting the Montreal Protocol phaseout requirements is summarized in the following table.

More about the HCFC Allowance System

Common HCFCs and Their Uses

Common HCFCs include:

• HCFC-22: used as a refrigerant in several applications such as unitary air conditioners, cold storage, retail food refrigeration equipment, chillers, and industrial process refrigeration. Also historically used (in smaller quantities) as a blowing agent for certain foam applications and as a propellant in aerosols.
• HCFC-141b: used as a blowing agent in rigid polyurethane foams and integral skim foams and in aerosol solvent cleaning applications.
• HCFC-142b: used as a blowing agent in extruded polystyrene boardstock. Also used in small quantities in refrigerant blends and as a retrofit refrigerant, such as in motor vehicle air conditioners that previously used chlorofluorocarbonchlorofluorocarbonA compound consisting of chlorine, fluorine, and carbon. CFCs are very stable in the troposphere. They move to the stratosphere and are broken down by strong ultraviolet (UV) light, where they release chlorine atoms that then deplete the ozone layer. CFCs are commonly used as refrigerants, solvents, and foam blowing agents. The most common CFCs are CFC-11, CFC-12, CFC-113, CFC-114, and CFC-115. The ozone depletion potential (ODP) for each CFC is, respectively, 1, 1, 0.8, 1, and 0.6. A table of all ozone-depleting substances (http://www.epa.gov/ozone/science/ods/index.html) shows their ODPs, global warming potentials (GWPs), and CAS numbers. CFCs are numbered according to a standard scheme (http://www.epa.gov/ozone/geninfo/numbers.html). (CFC)-12.
• HCFC-123: used in centrifugal chillers and portable fire extinguishers.
• HCFC-124: used in some sterilant mixtures and as a component in some CFC-12 retrofit refrigerants. Can be used as a retrofit to replace CFC-114 in some heat pumps and special air conditioning equipment.
• HCFC-225ca and HCFC-225cb: used as a solvent and aerosol solvent. Also historically used in small quantities in adhesives, coatings, and inks.
• HCFC-21: used as a refrigerant in highly specialized cooling loops.

The phaseout restricts the use of these HCFCs, and EPA continues to evaluate HCFC alternatives through its Significant New Alternatives Policy (SNAP) program.